Great question -- thank you!
Yes, you can take management action against the person who makes a harassment or discrimination complaint after being put on a performance improvement plan (PIP).
You just want to clearly outline that the PIP came first; the complaint came second; you investigated the complaint and found it lacked merit and now it's time to focus on business issues, including the substandard performance.
Your communication should summarize the situation and the timeline very clearly so that any third person can get a quick read on the situation and see that your process has been fair.
Employment Law Expert
February 9 2018